The present invention relates generally to graphical controllers, and more particularly relates to a graphical controller interface for monitoring multiple chemical feed constituents, such as for monitoring chloramination of a municipal water supply.
Disinfection chemicals such as chlorine, chloramines, chlorine dioxide, hydrogen peroxide, and the like, commonly are added to raw water to make it safe to drink. Chlorine is one of the most common disinfectants but due to health problems associated with disinfection byproducts such as trihalomethanes, many water producers are changing over to products such as chloramines (chlorine combined with ammonia).
Chloramination can be difficult to control because of the formation of monochloramine and the subsequent formation of dichloramine and trichloramine as the proportion of chlorine to ammonia exceeds the stoichiometric ratio of approximately 5 to 1 (by weight). Chloramine is currently commonly measured by a chlorine monitor, and as the chlorine to ammonia ratio rises above 5:1 (by weight), the measured chlorine level drops until the ammonia has been completely reacted and destroyed (breaking to free chlorine), at which time the total chlorine residual begins to rise again. An operator observing a total chlorine monitor can therefore read the same level of measured total chlorine for up to three different chlorine feed rates and be unsure where they are in the process. The objective with chloramine disinfection is to maximize the yield of monochloramine, without forming dichloramine or trichloramine, which have odor and taste concerns. Breaking to free chlorine may be used to remove chloramines from purchased water or to “shock” some distribution systems as part of a maintenance program.
Currently water chloramination disinfection operators are required to take readings from multiple analyzers and infer whether the stage of chloramination indicates monochloramine production, monochloramine destruction, free chlorine, and the like. For example if ammonia is present, the process is either in monochloramine production or destruction; if no ammonia is present and free chlorine is present, then the process has exceeded the “breakpoint,” and no chloramines remain. Water disinfection operators are frequently confused as to the meaning and interaction of the multiple analyzer readings, and may not have the ability to infer the correct stage in the chloramination process.
Another known method for monitoring water chloramination involves adding a color-forming reagent that reacts with monochloramine to a sample of the water, allowing the sample to be calorimetrically analyzed to determine the amount of monochloramine present. However, the method uses toxic chemicals, and the time for analysis to be completed is excessive for many control system applications. Another water chloramination control system is known that compares the concentration of aqueous higher chloramines to aqueous ammonia to optimize the ratio of added ammonia to chlorine, using spectroscopic measurements of free iodine produced from the reaction of potassium iodide with chlorine and monochloramine.
Chloramination control varies from water treatment agency to agency and in many cases must be inferred by calculation with the data available, and in many cases is poorly controlled, resulting in overfeed of ammonia or chorine, which can result in control problems causing nitrification (and bacterial growth), or taste and odor problems, respectively, or in the worst case, inadequate disinfection of the public water supply. There is consequently a need for a graphical controller for monitoring multiple chemical feed constituents, which would allow for improved control of chloramination. The present invention addresses this and other needs.